1. Field of the Invention
The present invention relates generally to a process for the production of diisobutene (DIB) wherein tertiary butyl alcohol (TBA) is used to modify an acid catalyst to provide more selectivity to the dimer. More particularly the invention relates to a process wherein the TBA and DIB are removed together as bottoms from a debutanizer column.
2. Related Art
One process for the dimerization of isobutene over an acid catalyst in the presence of tertiary butyl alcohol is disclosed in U.S. Pat. No. 4,100,220. The tertiary butyl alcohol is said to dehydrate the catalyst and provide for improved selectivity to the dimer.
Another liquid phase process for the oligomerization of C4 and C5 isoolefins is disclosed in U.S. Pat. No. 5,003,124 wherein the reaction mixture is allowed to boil to remove the heat of reaction and a further dimerization is obtained in a reactive distillation column. U.S. Pat. No. 4,242,124 discloses the reaction of isobutene with itself in a catalytic distillation column reactor to form diisobutene.
When tertiary butyl alcohol is used to improved the selectivity and separated from the unreacted C4""s by fractional distillation, then all components boiling heavier than C4 and lighter than DIB (referred to as heavies) may be removed along with the TBA and an azeotropic mixture of DIB. Since most feeds have at least some of these heavies, their build up must be prevented in the TBA recycle loop. A purge necessarily containing some TBA and DIB product is preferably withdrawn from the TBA loop. The purge represents a loss of isobutene (as TBA), a loss of feed heavies which might otherwise join the DIB in the gasoline pool, and some DIB product itself. Thus, the removal of the TBA from the DIB and heavies would be desirable.
Briefly the present invention comprises the removal of TBA from a first hydrocarbon stream into a water stream by contacting said streams under conditions of temperature and pressure to achieve extraction of said TBA into said water stream, and preferably the recovery of said TBA from said water stream by contacting said water steam containing said TBA with a second hydrocarbon stream under conditions of temperature and pressure to achieve extraction of said TBA into said second hydrocarbon stream. In a further preferred embodiment the TBA is a process enhancer in a process from which the first hydrocarbon stream originates and in a still further preferred embodiment the second hydrocarbon stream is a feed to the process from which the first hydrocarbon stream originates. Thus in a most preferred embodiment the TBA enhancer is removed from the product hydrocarbon stream of a process by contact with water into the water and then removed from the water by contact with the hydrocarbon feed into the hydrocarbon feed to the process from which the first hydrocarbon stream originated.
As used herein the term xe2x80x9cTBA enhancerxe2x80x9d means the TBA has a favorable effect on the process in question. The TBA may act as a homogeneous catalyst or catalyst modifier, although it may not be a reactant in the process. The TBA is present in very small amounts, usually in molar amounts of less than the reactant material, preferably a mol ratio of 0.001 to less than 1 mol of TBA/mol of reactants.
In a particular embodiment the present invention comprises the dimerization of isobutene over an acid catalyst in the presence of tertiary butyl alcohol (TBA). After the product diisobutene (DIB) and TBA has been separated from the unreacted C4""s, the bottoms containing the TBA, DIB and heavies are washed with water in a liquid/liquid contact column to remove the TBA in the water phase. The DIB and heavies may then be sent to gasoline blending or for further processing. The TBA/water stream is then reextracted with a hydrocarbon stream, preferably C4 feed, to remove and recycle the TBA.
The dimerization reaction may be effected in a standard single pass downflow fixed bed reactor, a distillation column reactor or combination as disclosed in U.S. Pat. No. 5,003,124 which is hereby incorporated by reference.
The term xe2x80x9creactive distillationxe2x80x9d is used to describe the concurrent reaction and fractionation in a column. For the purposes of the present invention, the term xe2x80x9ccatalytic distillationxe2x80x9d includes reactive distillation and any other process of concurrent reaction and fractional distillation in a column, i.e., a distillation column reactor, regardless of the designation applied thereto.
The catalyst beds as used in the present invention may be described as fixed, meaning positioned in a fixed area of the column and include expanded beds and ebulating beds of catalysts. The catalysts in the beds may all be the same or different so long as they carry out the functions of dimerization and hydrogenation as described. Catalysts prepared as distillation structures are particularly useful in the present invention.